1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to designs of shear blades that more securely shear a tubular.
2. Discussion of the Background
During the past years, with the increase in price of fossil fuels, the interest in developing new production fields has dramatically increased. At the same time, the equipment for extracting the oil is undergoing continuous changes for becoming more effective and reliable. A ram blowout preventer (BOP) is used in most wells for ensuring that the wells are closed in the event that a high pressure develops inside the wells or when various tests are conducted or when equipment above the BOP needs to be replaced or removed. Thus, the BOP is configured to act as a valve. Shear BOP are configured to not only close the well but also cut any tubular or tools that may be present inside the well.
For example, it may happen that during drilling, while the drill string is inside the well, a high pressure pocket is intersected by the drill. In this case, the shear ram BOP is used to cut the drill string to seal the well to prevent the high pressure from propagating to the rig above for safety reasons. The shear ram BOP traditionally includes two blades that move towards each other for shearing the tubular. However, there are instances when the existing blades are not capable of shearing the tubular or tools inside the well, thus failing to seal the well. This failure to shear the tubular may result in catastrophic events that may destroy the rig and may result in loss of human lives. For a better understanding of how the blades shear the tubular, a BOP is discussed next.
A shear ram BOP is shown in FIG. 1. A BOP 16 is shown having ram blocks 20. The ram blocks 20 are configured to move, when actuated by a rod 22, inside a first elongated cavity 24. The first elongated cavity 24 extends along a first axis X. A second elongated cavity 26 extends along axis Y, substantially perpendicular to and intersecting the first elongated cavity 24. The ram block 20 may include a shear blade 28 that is configured to cut a tubular 30 that may be present inside a well 32. The shear blade 28 may have a sharp edge that effectively cuts tool 30 when necessary. Another similar shear block and shear blade may be provided in an opposite region of the first elongated cavity 24.
A more detailed view of the ram block 20 and the shear blade 28 is shown in FIG. 2. The shear blade 28 is shown detached from the ram block 20. To attach the shear blade 28 to the ram block 20, a plurality of screws 36 are used. Corresponding holes 38 are formed in a frontal face 40 of the ram block 20. The sharp edge 42 of the shear blade 28 is configured to shear the tool. The thicker the tools provided inside well 32, the more powerful ram blocks 20 and blades 28 need to be provided to resist to the high pressures present inside the BOP when cutting the tool. Such pressure may be between 2,000 and 25,000 psi.
A top view of a pair of conventional shear blades 28 is shown in FIG. 3. It is noted that the two blades 28 are symmetrical and have two cutting edges 44 and 46 that make a large angle α between 120° and 180°. These edges may determine the tubular to move to a central position. However, these cutting edges may fail to shear the tubular if the walls of the tubular are strong or the size of the tubular is larger than a certain value.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.